Yeager,
I would test depending on what you want to demonstrate. If you want to test 180 degree flat reversals or 360 degree turns, that will give you some idea about energy retention in maneuvers. What wells has done is great stuff, but I think some testing on how much speed is lost in a flat turn would be useful.
The setup is the tricky part, but here is one suggestion:
Log into the TA.
Grab a plane, 100% fuel, most common ordinance load, but clean config.
Pick a big flat area with some visible landmarks, a 0 alt. main base works well.
Stay within 1k of the ground, a few hundred feet is better, as close as you can.
Trim the aircraft to a particular speed that all of the aircraft you test can reach in level flight, say 250 mph.
Line up with a landmark, then turn 360 degrees pulling a constant G load, say 4 G's, or whatever is most appropriate.
Record the times to make that 360 and the exit speeds.
FILM the tests so you can show Pyro if you find something. Also, you could skip recording any numbers in the tests this way, and just go back and look at the film after if you like. The film updates may not be fast enough for the accuracy you need though.
You could do these tests with and without combat trim if you have time, or just one way as long as you are consistent.
BTW, about the fuel multiplier issue. Your 1:1 fuel multiplier is not really correct. These planes would fly for MUCH longer in the real world, we burn fuel much faster in AH to account for the terrain being smaller. It has to be this way or it would take to long to find a fight. We can't have 5 hour combat sorties in the game.

I'd test in the TA to eliminate this issue all together. In addition, this way the tests are done online, so it's real in-game conditions with the real host instead of using the client side mini-host.
------------------
Lephturn - Chief Trainer
A member of The Flying Pigs
http://www.flyingpigs.com 
"My P-47 is a pretty good ship, she took a round coming 'cross the Channel last trip.
Just thinking 'bout my baby and lettin' her rip, always got me through so far."
- Steve Earl